In the modern communications space, data communications networks are normally deployed on a physical layer network infrastructure constructed using network nodes interconnected by high-speed (frequently optical) data communications links. In many cases, the nodes and links are arranged in comparatively simple ring architectures, such as Bi-directional Line Switched Rings (BLSRs). However, data communications networks are rapidly evolving toward more complex topologies, such as multiple highly interconnected rings, and/or mesh networks. With any network topology, reliability is primarily a product of resource redundancy and rapid physical fault detection and signal switching to avoid failed network resources.
Resource redundancy refers to communications bandwidth capacity and equipment that is held in a dormant (i.e., unused) state during normal operations of the network, so that it is available to carry traffic in the event of a network resource failure. In BLSR networks, a 1:1 ratio is typically maintained between redundant (usually referred to as “protection”) and working capacity. In mesh networks, the ratio between protection and working capacity is frequently 1:N, where N>1. In all cases, at least some redundant bandwidth capacity is maintained for each link, so that upon detection of a network resource failure affecting a working channel of that link, traffic can be switched onto the redundant capacity to bypass the failed resource.
Resource failure detection and switching of traffic into redundant resources (commonly referred to as “protection switching”) can normally be performed by any node of the network, and thus can occur in the nodes immediately adjacent the failed resource. Typically, protection switching is accomplished using either the switch core of the node, and/or special purpose switch elements external to the switch core. An example of the latter arrangement is described in Canadian Patent Application No. 2,275,606, entitled “Automatic Protection Switching System in a Network”, which was filed by Ellinas et al. on Dec. 20, 1996 and published on Jul. 2, 1998.
In all cases, the protection switching function operates to route traffic into a protection channel upon detection of any resource failure affecting normal traffic flow through a link or path. Normally, no distinction is made concerning which resource has failed. Thus, for example, the protection switching function is normally the same, whether the failed resource is a fiber span between two nodes, or an Optical-to-Electrical/Electrical-to-Optical (OEO) interface traversed by a traffic stream within one of the involved nodes.
This arrangement suffers the limitation that the probabilities of failure of the various components forming a link (and in particular OEO interfaces and optical fiber) can vary markedly. In particular, optical fiber tends to have a higher probability of failure (due to accidental fiber cuts) than an OEO interface, which is enclosed within the controlled environment of a node. Accordingly, based on their respective different probabilities of failure, an optimum network architecture would include respective different ratios of working to redundant resources for fiber and interfaces. However, in practice, each channel within a fiber must be hosted by a respective interface. Accordingly, redundant interfaces must necessarily be provisioned in the same ratio as redundant channels within a link. This typically results in greater numbers of redundant interfaces than is optimum, based on the probability of failure of each interface. This, in turn, tends to increase the size and cost of provisioning a network node having a desired working bandwidth capacity. The cost of provisioning the required number of interfaces typically constitutes the single largest component of the capital cost of deploying a modern fiber communications network.
Accordingly, a system that reduces the cost of a fiber communications network by enabling optimized provisioning of redundant resources remains highly desirable.